In order to prevent malfunctions or shutdowns when at least a part of a device is heated to a high temperature because of its high output, conventional semiconductor devices and vehicle-installed components are designed to propagate or release heat from Cu heat spreaders or Al radiator fins or to substrates or housings. Thus, metals or carbides having high thermal conductivity are used as materials for heat transmission and heat dissipation.
Patent Literature 1 proposes a structure including a first layer made of nanocarbon and a second layer made of an amorphous silicon material on the first layer. This configuration improves the crystallinity of nanocarbon in the first layer and improves thermal conductivity in the layer, achieving a smaller size than in a conventional heat transfer module. In this method, the first layer has thermal conductivity of about 950 W/mk to 1600 W/mk in an in-plane direction and thermal conductivity of 1.5 W/mk to 3.0 W/mk in a thickness direction, efficiently propagating and diffusing heat from a heated portion in the in-plane direction through the first nanocarbon layer. However, the nanocarbon layer and the amorphous silicon layer each have a small thickness of 1 nm to 20 nm, which is not large enough to propagate a large amount of locally generated heat.
This structure is manufactured by a thin-film process (vacuum device), and thus a long time period is necessary for increasing the thickness, causing the structure to be unsuitable for propagating a large amount of heat.
Furthermore, distortion may be created between the nanocarbon layer and the amorphous silicon layer by a stress generated according to a difference in thermal expansion coefficient between the layers in a heat cycle of heating and cooling when a device or electronic equipment is driven. Thus, cracking or peeling is highly likely to occur. The nanocarbon layer in particular, which is highly crystalline, has relatively low adhesion strength between the layers and thus is likely to reduce the reliability of the device and electronic equipment.
Patent Literature 2 describes a metal-graphite composite including a metallic thin film on at least one surface of a graphite film. The metallic thin film contains nickel, cobalt, or titanium or an alloy mainly composed of the metal, achieving excellent thermal conduction along a carbon-atom binding surface, electrical conductivity perpendicularly to the binding surface, and higher solderability on the metallic film.